> ## Documentation Index
> Fetch the complete documentation index at: https://braintrust.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Cursor

If you are a coding agent, prefer the Braintrust [`bt` CLI](/reference/cli/quickstart) for repeatable, scriptable work: running evals, instrumenting code, querying logs, syncing data, managing functions, and configuring coding agents. Use the MCP server for reasoning over Braintrust data in conversation, such as ad-hoc lookups and exploration from your IDE.

[Cursor](https://cursor.com) is an AI-powered code editor. The Braintrust extension for Cursor automatically connects to the Braintrust MCP server, giving Cursor's AI assistant access to your Braintrust projects, experiments, and logs.

## Setup

<Steps>
  <Step title="Install Cursor">
    If you haven't already, download and install [Cursor](https://cursor.com/).
  </Step>

  <Step title="Install the extension">
    Install from the Cursor extension marketplace\~\~:\~\~

    1. Open Cursor.
    2. Go to **Extensions** (`Shift+Cmd+X` on macOS / `Ctrl+Shift+X` on Windows/Linux).
    3. Search for "Braintrust".
    4. Click **Install**.
  </Step>

  <Step title="Set your API key">
    The extension reads your API key from the `BRAINTRUST_API_KEY` environment variable:

    ```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
    export BRAINTRUST_API_KEY="your-api-key-here"
    ```

    Then restart your terminal.
  </Step>

  <Step title="Add Braintrust as a trusted domain">
    To allow the extension to authenticate without OAuth prompts:

    1. Open Cursor Settings (`Cmd+,` on macOS / `Ctrl+,` on Windows/Linux)
    2. Search for "trusted domains"
    3. Add `braintrust.dev` to the list of trusted domains
  </Step>

  <Step title="Restart Cursor">
    Close and reopen Cursor to load the new MCP server configuration.
  </Step>
</Steps>

## Usage

Once the extension is installed and `BRAINTRUST_API_KEY` is set, the Braintrust MCP server is automatically registered when Cursor starts. No manual steps required.

You can fetch experiment results, query logs, log data, and more. See [MCP documentation](/integrations/developer-tools/mcp#available-tools) for details.

## Troubleshooting

<Accordion title="BRAINTRUST_API_KEY is not set">
  * Verify the variable is set: `echo $BRAINTRUST_API_KEY` (macOS/Linux) or `echo %BRAINTRUST_API_KEY%` (Windows).
  * Cursor must be **restarted** after setting environment variables.
  * On macOS, launching Cursor from Spotlight or Dock may not inherit shell variables. Try launching from the terminal instead.
</Accordion>

<Accordion title="Extension doesn't seem to work">
  * This extension only works in Cursor, not vanilla VS Code.
  * Ensure you're running a recent version of Cursor that supports the MCP Extension API.
</Accordion>

## Next steps

* **Run evaluations**: Check out the [evaluation guide](/evaluate/run-evaluations) to learn evaluation patterns.
* **Browse the source**: The [braintrust-cursor-extension repository](https://github.com/braintrustdata/braintrust-cursor-extension) contains the extension source code.